1. Field of the Invention
The present invention relates to an optical element holder and an optical communication module to which an optical element is mounted using the optical element holder.
2. Description of the Related Art
Recently, high-speed and large-capacity optical communication systems have further been advanced. Therefore, optical communication modules such as semiconductor laser modules and light-receiving modules used for the optical communication systems are required to have a higher reliability. In order to achieve the high reliability, generally and widely used is a method in which the optical elements constituting the optical communication module, such as an optical lens and an optical fiber, are fixed by a laser welding (YAG welding).
As shown in FIG. 1, an optical communication module 80 disclosed in Japanese Unexamined Patent Publication No. 63-219186, comprises a laser element 81, a lens 82, a U-shape holder 90, an optical isolator 83, an element carrier 84, a Peltier element 85, a lens 86, a ferrule 87, an optical fiber 88, a package 89 and the like.
Inside the package 89, the element carrier 84 is mounted through the Peltier element 85. On the element carrier 84, the laser element 81, the lens 82 and the optical isolator 83 are mounted and laser light outputted from the laser element 81 is coupled to the optical fiber 88. The optical fiber 88 is held by the ferrule 87 and the lens 86 is attached on the input side of the optical fiber 88.
Signal light is outputted from the laser element 81 and the signal light is guided to the optical isolator 83 through the lens 82. The signal light permeated through the optical isolator 83 enters into the optical fiber 88 through the lens 86. In this case, the return light from the optical fiber 88 is hindered by the optical isolator 83.
In order to compose the optical module, first, weld parts 94a, 95a of the U-shape holder 90 are laser-welded to the element carrier 84. Then, weld parts 96a, 97a, which are provided in a frame of the lens 82, are laser-welded to the U-shape holder 90. At last, weld parts 98a, 99a of the optical isolator 83 are laser-welded to the element carrier 84.
Next, a specific example of the conventional U-shape holder 90 will be described. Japanese Unexamined Patent Publication No. 08-5876 and the like disclose examples of the U-shape holder 90.
As shown in FIG. 2, in the conventional U-shape holder 90, a pair of opposing holding sections 92a, 92b are provided being projected on the surface side of a plate-type pedestal 91 so as to hold the lens 82 by the inner side of the two opposing holding sections 92a, 92b. At the same time, the weld parts 94a, 95a provided on the outer side of the holding sections 92a, 92b are laser-welded to the element carrier (element carrier 84 in FIG. 3A).
In this case, the U-shape holder 90 is mounted on the element carrier 84 while the lens 82 is being inserted between the opposing holding sections 92a, 92b of the holder 90 (FIG. 2). Then, in the state where the lens 82 is disposed in front of the laser element 81, the position of the holder 90 is adjusted in the X-axis direction as shown in FIG. 3A while making the laser element 81 emit the light so as to adjust the position of the lens 82 in the optimum position in the X direction. In this state, the weld parts 94a, 95a of the holder 90 are laser-welded to the element carrier 84 so as to fix the position of the lens 82 in the X direction.
Subsequently, as shown in FIG. 3A, the lens 82 is moved in the vertical direction (Y direction) between the opposing holding sections 92a, 92b so as to adjust the lens 82 to be in the optimum position in the Y direction. Further, as shown in FIG. 3B, the lens 82 is moved in the back-to-front direction (Z direction) along the optical axis direction of the lens 82 between the opposing holding sections 92a, 92b so as to adjust the lens 82 to be in the optimum position in the Z direction.
At the point where these adjustments of the positions are completed, the frame (not shown) supporting the lens 82 is laser-welded to the holder 90.
However, there are following shortcomings in the conventional U-shape holder 90. The shortcomings are emphasized in FIG. 4 and they are to be described by referring thereto.
As shown in FIG. 2 and FIG. 4, the bottom ends of the holding sections 92a, 92b of the holder 90 are welded to the element carrier 84, thereby forming the weld parts 94a, 95a between the bottom ends of the holding sections 92a, 92b and the element carrier 84. In these weld parts 94a, 95a, a welding stress as shown by an arrow is generated when being shrunk after the welding. The welding stress is generated when the inner structures of the holder 90 and the element carrier 84 are pulled towards the weld parts 94a, 95a sides. In this case, the mass of the element carrier 84 is sufficiently large as compared to that of the holder 90 so that it is hard to be affected by the welding stress. On the other hand, the holder 90 is formed in a forked shape. Therefore, when there is the welding stress generated in the bottom ends of the holding sections 92a, 92b, as shown in FIG. 4, the opposing holding sections 92a, 92b are deformed curving towards the outer side being away from each other due to the welding stress.
When adjusting the lens 82 to be in the optimum position in the Y direction and Z direction as shown in FIG. 3A and FIG. 3B, the two holding sections 92a, 92b as the reference are deformed by the welding stress as shown in FIG. 4. Thus, it is impossible to adjust the lens 82 to be in the optimum position in the Y direction and Z direction.
Further, when the holding sections 92a, 92b are deformed by receiving the welding stress, the top ends of the two holding sections 92a, 92b are deformed in the expanding direction as shown in FIG. 4 since they are formed in a forked shape.
When a frame 82a for supporting the lens 82 is welded to the two holding sections 92a, 92b, a clearance 96 is formed between the frame 82a and the holding sections 92a, 92b. Due to the clearance 96, when welding the frame 82a for supporting the lens 82 to the holding sections 92a, 92b, weld part 97b for welding therewith is formed inside the clearances 96. Thus, the frame 82a cannot be successfully welded to the holding sections 92a, 92b, which causes a trouble when determining the position of the lens 82.
In Japanese Unexamined Patent Publication No. 08-5876, the two holding sections 92a, 92b are curved to be in a convex shape towards the inner side, respectively. The frame of the lens is pinched between the two curved holding sections 92a, 92b to be welded. Further, in Japanese Unexamined Patent Publication No. 08-5876, as shown by an alternate long and short dash line in FIG. 2, projection parts 100 are projected in the lateral direction being away from the holding sections 92a, 92b. 
In Japanese Unexamined Patent Publication No. 08-5876, the reason for projecting the projection parts 100, 100 in the lateral direction may be as follows. That is, weld parts 94a′, 95a′ for welding the projection parts 100 to the element carrier 84 are brought away from the holding sections 92a, 92b as much as possible by separating the projection parts 100, 100 away from the holding sections 92a, 92b so as to minimize the welding stress affected on the holding sections 92a, 92b, which is generated when welding the projection parts 100 to the element carrier 84. It is true that the affect of the welding stress is minimized through the configuration in which the above-described projection parts 100 are provided. However, in order to minimize the affect of the welding stress as much as possible, the forming positions of the projection parts 100 with respect to the holding sections 92a, 92b are required to be separated away as much as possible. With the configuration, the external dimension of the U-shape holder 90, especially the dimension in the lateral direction, is expanded so that the area occupied for disposing the holder 90 becomes large. Thus, it becomes impossible to meet the demand for reducing the dimension of the optical communication module using the holder 90.